Operators, owners, and facility designers of indoor farms know that climate management is one of the most challenging aspects of growing healthy and productive crops. The big question is, why is it so hard to manage the indoor plant environment? The answer lies at the intersection between plants, technology, and people.
It’s essential to recognize that the primary occupant is a plant, typically many plants. In an indoor farm, managing humidity and temperature is critical to the health and development of plants. Plants do not go home at night, and they do not go to the office in the morning. Plants interact with interactive building systems.
The plants have changing and fluctuating needs over time, both on a daily basis (photoperiod vs. dark period) and on a weekly or monthly basis (vegetative vs. flowering stages). They are frequently grown in the same spot in the room and can’t get up to change the thermostat (or humidistat) on the wall when it gets too cold or too humid.
All these factors require the engineering of HVAC systems that can monitor and respond to – even predict – the changes in the indoor plant environment.
Designed for commercial and residential applications, conventional HVAC systems primarily focus on temperature management. Building codes have driven HVAC systems toward energy efficiency to reduce carbon emissions and reduce the demand on power supplies.
Energy-efficient HVAC systems are very good at temperature control. However, less coil depth and greater coil spacing (along with lower refrigerant suction pressure differentials) reduce their capacity to remove moisture. Additionally, most HVAC equipment is designed assuming it does not need to operate at full capacity all day and all year long. But indoor farms never rest and are expected to operate year-round, rain or shine, freezing cold or oppressively humid. As a result, running compressors for cooling and dehumidification under low-ambient conditions can result in failures without implementing the proper safeguards. Further, their constant operation and cycling to meet changing room conditions can wear down equipment quickly, often resulting in frustratingly short equipment lifespans.
When it comes to managing the plant environment, HVAC equipment is generally slow to respond to instantaneous changes, such as turning lights on and off. They are also often controlled by a single sensor that may or may not represent the entire room environment and can’t easily manage multiple climate zones (and microclimates) without multiple units and additional costs.
One of the most significant barriers to getting HVAC right for indoor farms is the lack of knowledge and communication among growers, engineers, manufacturers, investors, and other stakeholders. Engineers are not growers, and the majority of them do not understand plants or the environments required to cultivate them. And growers are typically not engineers; they don’t understand thermodynamics, fluid dynamics, or the mechanics of how HVAC systems operate.
Education and communication between all parties will improve climate management of the indoor farm. Engineers and industry professionals who engage with growers to learn more about how the environment affects plant responses and why certain operating strategies are employed, will be in a better position to recommend HVAC equipment that can perform to a desired set of conditions.
Case in point, many manufacturers are actively developing new and modified HVAC equipment to meet the environmental control needs of the indoor farm. Engineers are also asking growers more questions about the lights they’re using, the expected irrigation rates, and operating schedules and room targets in an effort to specify and design better HVAC systems for both temperature and humidity control. In general, HVAC professionals who want to succeed in the controlled-environment agriculture market are asking more questions, seeking guidance from available literature and experienced professionals, and supporting new efforts to conduct research and educate the community.
Growers and investors, too, are becoming more educated and savvy about climate management, either through the hard-knocks of operating a farm with poor climate control, or by attending conferences and classes that focus on research and best practices for horticulture and cultivation. They are learning about the importance of managing vapor pressure deficit (VPD), day and night temperature differentials (DIF), and the daily light integral (DLI) to achieve specific plant responses and meet harvest schedules.
So why is it so difficult for HVAC to manage the indoor farm environment?
For many reasons: Because plants aren’t people, and many people do not understand plants; the indoor plant environment is dynamic and everchanging; the technology hasn’t caught up (yet) to the needs of the plant and grower; and climate management needs and HVAC capabilities (or the lack thereof) aren’t always well-communicated between grower and engineer.
Working together and learning from each other is key to the success of controlled environment agriculture (CEA) and indoor farming. Once we all share a common understanding of how plants respond to their environment, why growers are targeting certain conditions, and what are the capabilities and limitations of HVAC equipment, it will be easier to manage the indoor farm environment and grow healthy and productive plants, anytime and anywhere.
Dr. Nadia Sabeh (aka, “Dr. Greenhouse”) is the President and Founder of Dr. Greenhouse, Inc., a mechanical engineering firm specializing in the design of agricultural HVAC systems for indoor plant environments, including indoor grows, vertical farms, and greenhouses. Dr. Sabeh has designed specialized high-performance HVAC systems for plant-focused facilities across North America, Europe, the Middle East, and Asia. As the Principal of Dr. Greenhouse, Dr. Sabeh leads the company’s early-stage design charrettes, programming, mechanical systems design and integration and quality control of Construction Documents. For more than 20 years, Dr. Sabeh has helped farmers control their environments to grow indoor crops such as cannabis, strawberries, leafy greens, and vine crops in locations that, previously, would have been impossible or impractical. As a nationally recognized engineer, researcher and educator, Dr. Sabeh is a keynote speaker and leads expert panels at industry events and conferences. She also advises regulatory boards and standards developers, including serving as Chair of the co-sponsored committees from the American Society of Agricultural and Biological Engineers (ASABE) and the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) tasked with developing the standard “HVAC for Indoor Plant Environments Without Sunlight.” Dr. Sabeh has a robust online presence, including on YouTube and the popular “The Doctor Is In” podcast, where she interviews industry and academic leaders to discuss technology and innovation, emerging research and successful strategies in the design, construction, and operation of economically competitive facilities. Dr. Sabeh received her Ph.D. in Agricultural Engineering from the University of Arizona’s Controlled Environment Agriculture Center (CEAC) and is a Mechanical Engineer licensed in California and Ohio. See all author stories here.
The Voice for Controlled Environment Production